The invention relates to electrical devices containing a dielectric liquid such as capacitors and transformers wherein the dielectric liquid is essentially a particularly defined class of aromatic sulfides.
Until recent years, polychlorinated biphenyl (PCB) was widely used as a dielectric liquid in transformers and other such electrical devices. Although its physical and electrical properties made it a superior material for this kind of use, PCB was found to have highly undesirable biological effects and these and its resistance to degradation when it was allowed to contaminate the ground or bodies of water by spillage or by improper disposal caused a widespread search for other dielectric liquids with less objectionable properties.
Among the alternative liquids suggested for this use, chlorinated diphenyl oxides have many advantages in both their physical and their biological properties. However, concern about the biological effects of possible polychlorinated aromatic impurities in these materials has caused some delay and restriction in their use on a large scale.
Aromatic sulfones have also been proposed for use as dielectric liquids. These compounds have other disadvantages, however, including unusually high dielectric constants that may cause an unacceptably high level of electrical conductivity and also undesirably high melting or pour points. To avoid these disadvantages, various mixtures of aromatic sulfones with known dielectric liquids have been proposed. Since the suggested diluents usually include polychlorinated aromatic hydrocarbons, the original advantages of the sulfones as dielectric liquids are thus also diluted and lost.
Analogous aromatic sulfides are known and some of these have been proposed for use as functional fluids, for example, as synthetic lubricants, hydraulic fluids, and damping fluids. Fujisawa et al., U.S. Pat. No. 3,706,805 (see also related French Pat. No. 1,583,819) describes the preparation of aryl-sulfides by the reaction of various substituted aromatic hydrocarbons with a sulfur chloride in the presence of a metal or metal halide catalyst. The principal utilities taught for the resulting products are as fungicides and herbicides. Campbell et al., U.S. Pat. No. 3,538,166 describes another method for the preparation of aromatic and heterocyclic sulfides. The compounds shown are mostly halogenated and polynuclear sulfides and mixed ether-sulfides. The products are broadly described as functional fluids including dielectric fluids. However, the compounds shown typically have relatively high melting or pour points and some are solids at room temperature.